Here's the official version:
From my reading of it (and this is how I interpret it) it only says "you" as in not you and your descendants (if I missed that then tell me where), just you. In this regard iTunes Store purchases seem to be different from CDs.
There would also be technical difficulties. Purchases cannot be merged with other Apple IDs or transferred. Somebody would have to use your AppleID which is possible but would create management problems. Items could probably be shared with relatives but it would have to be done within the framework of Family Sharing which some may not wish to do.
I think it is wise you are thinking of a digital legacy because this is going to be a big 21st century issue. I am making up a document with my usernames and passwords.